Miniaturized affinity chromatography: A powerful technique for the isolation of high affinity GAGs sequences prior to their identification by MALDI-TOF MS

Glycosaminoglycans (GAGS) are involved in many biological processes through interactions with a variety of proteins, including proteases, growth factors, cytokines, chemokines and adhesion molecules. Identifying druggable GAG-protein interactions for therapeutic purposes is a challenge for the analytical community. In this context, this work investigates the use of a new miniaturized monolithic affinity column (poly(GMA-co-MBA) grafted with antithrombin III (AT III)) to specifically capture and elute high affinity sequences contained in low molecular weight heparin (enoxaparin) for further on-line characterization. This miniaturized, high binding capacity affinity column allows the specific capture of high-affinity oligosaccharide chains from Enoxaparin, even at low concentrations and with a minimal consumption of AT III. In addition to purification, this elution process enables preconcentration for direct analysis by capillary zone electrophoresis. It was found that many of oligosaccharide chains in enoxaparin were eliminated and that certain chain sequences were retained and enriched. Direct coupling with MALDI-TOF MS was successfully used to further characterize the specifically retained oligosaccharides where nano-ESI-TOF MS failed. After optimization of the sample preparation and ionization parameters, direct on-line analysis was performed by applying the elution volume released from the miniaturized affinity column (≤1 μL) directly to the MALDI plate. Finally, this original miniaturized analytical workflow coupling miniaturized AT III-affinity chromatography to MALDI-TOF MS detection is able to select, enrich and detect and identify high affinity sequences (mainly DP4 in size length with a high degree of sulfation) from low molecular weight heparin samples. A more specific selection of GAG sequences can be achieved by increasing the ionic strength during the washing step of affinity chromatography. This is consistent with the known binding pattern between heparin and AT III.

Preparation of miniaturized hydrophilic affinity monoliths: Towards a reduction of non-specific interactions and an increased target protein density

In affinity chromatography, non-specific interactions between the ligands and the affinity column may affect the results, leading to misinterpretations during the investigation of protein-ligand interactions (detection of false positives in ligand screening, lack of specificity in purification). Such non-specific interactions may arise both from the underlying support or from the target protein itself. If the second ones are protein-dependent (and cannot be studied in a general framework), the first ones occur in the same way regardless of the immobilized target. We propose a methodology to identify the origin of such non-specific interactions with the underlying material of the affinity column. This methodology relies on the systematic investigation of the retention behavior of a set of 41 low-molecular weight compounds covering a wide chemical space (net charge, log D, functionality). We first demonstrate that the main source of non-specific interactions on the most commonly used GMA-co-EDMA monolith comes from hydrophobic effects. To reduce such non-specific interactions, we developed a new hydrophilic glycidyl methacrylate-based monolith by replacing the EDMA crosslinker by the more hydrophilic NN' Methylenebisacrylamide (MBA). Optimization of the synthesis parameters (monomer content, initiation type, temperature) has focused on the reduction of non-specific interaction with the monolithic support while maximizing the amount of protein that can be grafted onto the monolith at the issue of its synthesis. The retention data of the 41 test solutes on the new poly(GMA-co-MBA) monolith shows a drastic reduction of non-specific interactions except for cationic compounds. The particular behavior of cationic compounds is due to their electrostatic interactions with carboxylic groups resulting from the partial acidic hydrolysis of amide groups of MBA during the epoxide ring opening step. So, the ring opening step in acidic media was replaced by a hot water treatment to avoid side reaction on MBA. The new monolith poly(GMA-co-MBA) not only has improved hydrophilic surface properties but also a higher protein density (16 ± 0.8 pmol cm^-1 instead of 8 ± 0.3 pmol cm^-1). To highlight the benefits of this new hydrophilic monolith for affinity chromatographic studies, frontal affinity chromatography experiments were conducted on these monoliths grafted with con A.

Lectin Affinity Chromatography

Glycosylation is a non-template-driven posttranslational modification during which linked-sugars and glycans are added to the nascent polypeptide. Over 70% of the eukaryotic proteome is thought to be glycosylated. It is now known that correct glycosylation is essential for the correct folding, solubility, stability, and immunogenicity of proteins. In this chapter, we describe the technique of lectin affinity chromatography (LAC), a procedure that has the ability to distinguish different glycans, which are attached to proteins or lipids, termed glycoproteins or glycolipids, respectively. This method utilizes different immobilized lectins that have affinity for specific sugar substrates, to separate a wide range of glycan-attached complexes (Ambrosi et al., Org Biomol Chem 3:1593-1608, 2005). To further enhance the specificity of LAC, a corresponding free sugar may be used to produce a specific elution. In general, the conditions under which lectin affinity chromatography operates are relatively mild resulting in good biological recoveries of the glycoproteins.

Development of a multi-layering protein grafting process on miniaturized monolithic columns for weak affinity nano liquid chromatography application purposes

Affinity chromatography is a powerful technique to identify and quantify weak ligand-protein interactions (Kd in the range of mM to 0.1µM). In some fields such as Fragment Based Drug Discovery, the detection of very weak affinities (mM) is of utmost importance since weak ligands can be good starting points for the conception of high affinity ligands. However, the identification of such weak ligands can be hampered by the limited bulk density of active target grafted onto the support. At the same time, downscaling the chromatographic column is of utmost interest when scarce and/or expensive proteins are targeted. In this context, we herein present a novel approach of protein immobilization to improve the bulk density of active protein grafted onto organic capillary monolithic columns. The proposed approach is based on the streptavidin-biotin interaction and consists of successive grafting steps of biotinylated target protein onto streptavidin layers through a multi-layering process. Concanavalin A was used as model protein. The study focuses on the optimization of the grafting conditions to maximize the amount of active protein during the multi-layering process and highlights the impact of the biotinylation ratio of the protein. It is demonstrated that a 3-layer grafting process allows to improve the bulk density of active sites by a 2-fold factor compared to a single layer. This improvement in protein density allows to increase the affinity range of this technique to the millimolar range.

Molecular recognition and interaction between human plasminogen Kringle 5 and voltage-dependent anion channel-1 by biological specificity technologies and molecular dynamic simulation

Voltage-dependent anion channel-l (VDAC-1) can bind with plasminogen Kringle 5 as the cell surface receptor and induce cell apoptosis, but the detailed information of binding is not clear yet. Thus, the mutual recognition and binding were investigated here utilizing frontal affinity chromatography, surface plasma resonance, mutation analysis combining molecular dynamics simulation. The results showed that Kringle 5 binds with VDAC-1 in equimolar driven mainly by electrostatic force, with 15 amino acid residues participating in Kringle 5 and 21 in VDAC-1. The observed conformational changes indicated the automatic structure regulation providing these two proteins suitable conformations and spatial surroundings for the tighter and stabler binding. Moreover, Glu29 in Kringle 5 was speculated as the key residue maintaining the largest energy contribution. Therefore, this work provided precise information for the recognition and binding of Kringle 5 with VDAC-1 that is valuable for the corresponding treatment of tumours or other angiogenic diseases.

Frontal affinity chromatography: An excellent method of analyzing weak biomolecular interactions based on a unique principle

BACKGROUND

Not only strong biomolecular interactions but also weak interactions play important roles in ensuring appropriate operations of many biological systems. Although a thorough investigation of the latter is essential in understanding life science, few suitable research tools are available because of inherent difficulties.

SCOPE OF REVIEW

Frontal affinity chromatography (FAC) is a versatile method that overcomes the inherent difficulties to provide accurate information on weak interactions. Since its concept and merit are not widely recognized, a comprehensive interpretation of FAC is provided in this review to encourage its application among researchers.

MAJOR CONCLUSION

FAC is based on a unique principle of measuring the binding strength by the delayed migration of an analyte through an affinity column. Its utility was elucidated via the lectin-glycan interactions.

GENERAL SIGNIFICANCE

FAC has a great potential as a research tool to solve many difficult problems in general bioscience that are relevant to almost all researchers.

Frontal Affinity Chromatography: A Highly Suitable Retardation Phenomenon-Based Research Tool for Analyzing Weak Interactions Between Biomolecules

The greatest advantage of frontal affinity chromatography (FAC) is that the analyte concentration does not need to be taken into consideration, and this renders FAC an extremely favorable analytical tool for weak interactions. In this short review, we propose a straightforward explanation of the underlying mechanism. When FAC is performed using analyte solutions at relatively high concentrations, concentration-dependent retardation is observed due to competition among analyte molecules, and the elution volume changes depending on the degree of saturation of the immobilized ligand.However, when the analyte concentration is very low, no competition occurs among the analytes, and the elution volume reaches a constant value, which reflects the proportion of bound state to free state of a single analyte molecule. Therefore, the binding strength can be determined using a minimum analyte concentration.

Biophysical Analyses for Probing Glycan-Protein Interactions

Glycan-protein interactions occur at many physiological events, and the analyses are of considerable importance for understanding glycan-dependent mechanisms. Biophysical approaches including 3D structural analysis are essential for revealing glycan-protein interactions at the atomic level. The inherent diversity of glycans suits them to function as identification tags, e.g., distinguish self from the nonself components of pathogens. However, the complexity of glycans and poor affinities for interaction partners limit the usefulness of conventional analyses. To cope with such troublesome glycans, a logical sequence of biophysical analyses need to be developed. In this chapter, we introduce a workflow of glycan-protein interaction analysis consisting of six steps: preparation of lectin and glycan, screening of glycan ligand, determination of binding epitope, quantitative interaction analysis, 3D structural analysis, and molecular dynamics simulation. Our increasing knowledge and understanding of lectin-glycan interactions will hopefully lead to the design of glyco-based medicines and vaccines.

Lectin Affinity Chromatography (LAC)

Many proteins are glycosylated, that is to say they have bound sugars or glycans. Glycosylation is a non-template-driven posttranslation modification. It is now known that correct glycosylation is essential for the correct folding, solubility, stability, and immunogenicity of proteins. Here, we describe the technique of Lectin Affinity Chromatography (LAC), a procedure that has the ability to separate different glycans which are attached to proteins or lipids, termed glycoproteins or glycolipids, respectively. This method utilizes different immobilized lectins that have affinity for specific sugar substrates, to separate a wide range of glycan-attached complexes (Ambrosi et al., Org Biomol Chem 3:1593-1608, 2005). To further enhance the specificity of LAC, a corresponding free sugar may be used to produce a specific elution. In general, the conditions under which lectin affinity chromatography operates are relatively mild resulting in good biological recoveries of the glycoproteins.

Development and characterization of the α3β4α5 nicotinic receptor cellular membrane affinity chromatography column and its application for on line screening of plant extracts

The α3β4α5 nAChR has been recently shown to be a useful target for smoking cessation pharmacotherapies. Herein, we report on the development and characterization of the α3β4α5 nicotinic receptor column by frontal displacement chromatography. The binding affinity of the nicotine and minor alkaloids found in tobacco smoke condensates were determined for both the α3β4 and α3β4α5 nicotinic receptors. It was demonstrated that while no subtype selectivity was observed for nicotine and nornicotine, anabasine was selective for the α3β4α5 nicotinic receptor. The non-competitive inhibitor binding site was also studied and it was demonstrated while mecamylamine was not selective between subtypes, buproprion showed subtype selectivity for the α3β4 nicotinic receptor. The application of this methodology to complex mixtures was then carried out by screening aqueous-alcoholic solutions of targeted plant extracts, including Lycopodium clavatum L. (Lycopodiaceae) and Trigonella foenum graecum L. (Fabaceae) against both the α3β4 and α3β4α5 nAChRs.

Penetrable silica microspheres for immobilization of bovine serum albumin and their application to the study of the interaction between imatinib mesylate and protein by frontal affinity chromatography

In the current study, novel featured silica, named penetrable silica, simultaneously containing macropores and mesopores, was immobilized with bovine serum albumin (BSA) via Schiff base method. The obtained BSA-SiO2 was employed as the high-performance liquid chromatographic (HPLC) stationary phase. Firstly, D- and L-tryptophan were used as probes to investigate the chiral separation ability of the BSA-SiO2 stationary phase. An excellent enantioseparation factor was obtained up to 4.3 with acceptable stability within at least 1 month. Next, the BSA-SiO2 stationary phase was applied to study the interaction between imatinib mesylate (IM) and BSA by frontal affinity chromatography. A single type of binding site was found for IM with the immobilized BSA, and the hydrogen-bonding and van der Waals interactions were expected to be contributing interactions based on the thermodynamic studies, and this was a spontaneous process. Compared to the traditional silica for HPLC stationary phase, the proposed penetrable silica microsphere possessed a larger capacity to bond more BSA, minimizing column overloading effects and enhancing enantioseparation ability. In addition, the lower running column back pressure and fast mass transfer were meaningful for the column stability and lifetime. It was a good substrate to immobilize biomolecules for fast chiral resolution and screening drug-protein interactions.

Purification of galectin-1 mutants using an immobilized Galactoseβ1-4Fucose affinity adsorbent

Galectins are a family of lectins characterized by their carbohydrate recognition domains containing eight conserved amino acid residues, which allows the binding of galectin to β-galactoside sugars such as Galβ1-4GlcNAc. Since galectin-glycan interactions occur extracellularly, recombinant galectins are often used for the functional analysis of these interactions. Although it is relatively easy to purify galectins via affinity to Galβ1-4GlcNAc using affinity adsorbents such as asialofetuin-Sepharose, it could be difficult to do so with mutated galectins, which may have reduced affinity towards their endogenous ligands. However, this is not the case with Caenorhabditis elegans galectin LEC-6; binding to its endogenous recognition unit Galβ1-4Fuc, a unique disaccharide found only in invertebrates, is not necessarily affected by point mutations of the eight well-conserved amino acids. In this study, we constructed mutants of mouse galectin-1 carrying substitutions of each of the eight conserved amino acid residues (H44F, N46D, R48H, V59A, N61D, W68F, E71Q, and R73H) and examined their affinity for Galβ1-4GlcNAc and Galβ1-4Fuc. These mutants, except W68F, had very low affinity for asialofetuin-Sepharose; however, most of them (with the exception of H44F and R48H) could be purified using Galβ1-4Fuc-Sepharose. The affinity of the purified mutant galectins for glycans containing Galβ1-4Fuc or Galβ1-4GlcNAc moieties was quantitatively examined by frontal affinity chromatography, and the results indicated that the mutants retained the affinity only for Galβ1-4Fuc. Given that other mammalian galectins are known to bind Galβ1-4Fuc, our data suggest that immobilized Galβ1-4Fuc ligands could be generally used for easy one-step affinity purification of mutant galectins.

Analysis of biomolecular interactions using affinity microcolumns: a review

Affinity chromatography has become an important tool for characterizing biomolecular interactions. The use of affinity microcolumns, which contain immobilized binding agents and have volumes in the mid-to-low microliter range, has received particular attention in recent years. Potential advantages of affinity microcolumns include the many analysis and detection formats that can be used with these columns, as well as the need for only small amounts of supports and immobilized binding agents. This review examines how affinity microcolumns have been used to examine biomolecular interactions. Both capillary-based microcolumns and short microcolumns are considered. The use of affinity microcolumns with zonal elution and frontal analysis methods are discussed. The techniques of peak decay analysis, ultrafast affinity extraction, split-peak analysis, and band-broadening studies are also explored. The principles of these methods are examined and various applications are provided to illustrate the use of these methods with affinity microcolumns. It is shown how these techniques can be utilized to provide information on the binding strength and kinetics of an interaction, as well as on the number and types of binding sites. It is further demonstrated how information on competition or displacement effects can be obtained by these methods.